The present invention generally relates to an automatic frequency control device which will not pull in the sound carrier in the adjacent receiving channel.
There has been known an automatic frequency control device for a television receiver of the type in which the oscillation frequency of a local oscillator is corrected in response to the output voltage derived by the FM detection of the video intermediate frequency signal.
However, the prior art automatic frequency control device of the type described has some defects. Firstly, it tends to pull in the sound carrier of the adjacent receiving channel because the inversed S-shaped character voltage is induced by the sound carrier of the adjacent receiving channel when the electric intensity thereof is high; when the oscillation frequency of the local oscillator is too low or deviates to a lower frequency by about 1.5 MHz. Secondly, when the oscillation frequency is too high or deviates to a higher frequency by more than 1.3 MHz, the video carrier drops at or in the proximity of the tuning frequency of 60.25 MHz of a sound carrier trap for the adjacent receiving channel so that the upper pull-in range is limited only to about 1.3 MHz. As a result, the erratic operations tends to occur very often.